Innate immunity has evolved as the first line defense against microbial proliferation and invasion on body surfaces through effectors that are preformed or available within hours. Much attention has been given to the epithelial cells lining mucosal body surfaces and to the overlaying fluid, which is rich in mucins and antimicrobial (poly) peptides, for example lysozyme. However, though all body fluids also contain lipids, including free fatty acids and phospholipids, only in the lung, surfactant factor associated with proteins has been welt documented as defense molecule. Supported by numerous reports of antimicrobial activity of fatty acids, alterations of fatty acid profiles in certain infectious diseases, documentation of an intestinal surfactant-like particle and our preliminary data indicating a synergism between lysozyme and selected fatty acids, we propose that lipids including free fatty acids secreted by epithelial cells are an indispensable arm of host defense acting independently or in synergy with other defense molecules. To test this hypothesis we will take 3 approaches with the following specific aims. We will determine whether: (1) Inhibition of epithelial lipid secretion leads to enhanced microbial proliferation, and (2) selective removal of lipids from nasal fluids will decrease the fluid's inherent antimicrobial activity, which can be reversed after resupplementation with the extracted lipids. Mucosal sites investigated will be the sino-nasal region and the genital tract. In vitro models will employ primary epithelial cells and existing immortalized. Cells will be cultured at an air-liquid interface in the presence of radioactively labeled lipids with and without pro-inflammatory stimuli or lipid secretion inhibitors. Lipids from normal nasal fluid will be selectively removed by solid phase extraction with C18-bonded silica and eluted with acetonitrile. Lipids will be identified and quantified using radiographs of developed TLC plates and mass spectrometry techniques. Antimicrobial activity of treated and untreated samples will be assessed by determination of CFUs and microbial metabolic activity using bacteria and yeasts that do not routinely cause infection in the healthy adult and a common STD pathogen. (3) Epithelial lipid effectors identified in aim 1 and 2 bind to the microbial target. Binding of candidate lipid effectors to microbes will be documented and quantified with radioactive binding studies employing liquid scintillation and radiolabeled lipids and with surface plasmon resonance spectrometry. This new concept in innate immunity may have major significance in infectious diseases through providing new aspects in hereditary predisposition to chronic infectious diseases and host pathogen interactions and initiating new approaches to drug development and nutritional recommendations.